After beer has been fermented in the beer brewing process, commercial beer producers and home brewers can use reusable steel kegs to store the fermented, uncarbonated beer. Kegs range in size from approximately two to sixteen gallons and are constructed to withstand pressure up to 130 PSI to enable holding the beer under pressure. The pressurization of the vessel serves multiple purposes. Pressurizing the keg with carbon dioxide is a method used to force carbonate the uncarbonated beer. After the beer is carbonated, the pressure can then be reduced to maintain the carbonation level and to facilitate serving the beer from the keg.
When the beer in the keg is to be served, the keg is placed in a vertical position so the gas inlet for pressurization and the beverage outlet port are physically located on the top side of the keg. The vertical orientation is necessary to enable dispensing all liquid in the keg because the internal liquid dip tube in fluid communication to the beverage outlet port is axially centered and extends to the base of the keg. If the keg were placed in a horizontal orientation, the last half of the liquid volume wouldn't be able to be evacuated from the keg because it would no longer be in fluid communication with the liquid dip tube after the fluid level goes below the liquid dip tube.
Prior to serving, the beer can be cooled in the kegs by placing the keg in a short-term ice bath or in a relatively expensive specialized, dedicated refrigeration system large enough to hold one or more vertical kegs. After the beer is cooled to serving temperature, it is then forced out of the keg via the pressurized gas connected to and entering the keg. The beer can be served from the keg using a number of different configurations including attaching a tap assembly or a liquid line to transfer the beer for dispensing. The liquid line would be connected to a simple faucet or to a more complex setup consisting of a tower assembly with one or more ornamental faucets which would be used to dispense the beer into a drinking glass.